For satellite operators who support remote satellite terminals with a very small aperture terminal (VSAT) system, setting the antenna polarization on the remote satellite terminal is necessary for interference free operation of the satellite communications payload that is operating on an opposite orthogonal polarization of the satellite. With a 2-port antenna feed in a typical low cost antenna, it is difficult for an installer commissioning the remote satellite terminal to determine empirically if the antenna polarization on the remote satellite terminal is correct. This is due to the broad nature of the co-polarization peak and the narrow nature of the cross polarization null with regards to the angular displacement of a linearly polarized feed on a typical satellite antenna system.
The relationship of how transmit polarization 12 and receive polarization 10 are adjusted around the boresite of the antenna 32 is provided in FIG. 1. As indicated by arrow 13, rotation of the satellite antenna feed system 33 effects the transmit/receive polarizations 12, 10 of the antenna 32 around the boresite.
The correct polarization angle is defined as the angle at which the remote satellite terminal polarization characteristics of the signal transmitted by the antenna are aligned with the polarization characteristics of the antenna system on the satellite being accessed. Ideally, the co-polarized receive gain and cross polarized transmit gain of the VSAT system exactly matches the rotational angle of the satellite antenna feed system.
An incorrect polarization setting between a remote satellite terminal and a satellite is shown in FIG. 2. The co-polarization receive gain is indicated by reference 10 and the cross polarization transmit gain is indicated by reference 12. The satellite polarization setting 11 is offset from the feed polarization angle 6 at the satellite, as indicated by reference 14. Similarly, the co-polarization receive gain 10 is offset from the feed polarization angle displacement θ at the satellite, as indicated by reference 15.
Since the co-polarization receive gain 10 exhibits a very broad peak for receiving an acquisition signal from the satellite, the offset 15 minimally impacts reception of the acquisition signal. However, this offset 14 for the cross polarization transmit gain 12 causes a significant amount of energy to be transmitted into the opposite polarization, which causes cross polarization interference at the satellite.
To alleviate this issue with large populations of mobile VSAT systems, the normal practice is for the installer to call to a Network Operations Center (NOC), and under instruction from an operator, set the polarization with the operator. The operator has access to an earth station antenna fitted with the equipment to see signals on both polarizations.
The operator feeds back the empirical observation of the relative levels of the desired (co-polarized) signal and the undesired (cross polarized) signal. Frequencies are set aside on satellites for this application. Since the signals used for the measurement are typically single frequency sinusoidal (known as continuous wave or CW) and are generated by the transmission apparatus of the terminal, the VSAT terminal can not carry any traffic in this state. Therefore, communications between the installer and the operator requires a communications channel separate from the normal VSAT bearer channel.
As the number of VSAT systems have increased, and, in particular, VSAT systems that are in a semi-mobile (also known as nomadic) operation, the burden on network operators and installers with this polarization setting technique has increased dramatically. Since one space segment resource and one network operator is occupied full time for approximately 30 minutes, the technique is very difficult and expensive to scale.
In addition, since there is no mechanism to enforce the installer setting the cross polarization on the VSAT system, there has also been an increase in the number and severity of incidents of interference on the opposite polarization. Installers will simply point the antenna at the satellite and once the electronics package joins the network, they think that they are done. Very often, the remote satellite terminal with an incorrect polarization setting will operate satisfactorily on co-polarized receive due to the broad nature of the co-polarization peak, but the cross polarized transmit gain is not aligned correctly, as illustrated in FIG. 2. This offset results in the cross polarized transmit gain causing cross polarization interference on the opposite polarization at the satellite. The cross polarization interference needs to be resolved, which is an even more difficult and expensive analysis and remediation process.
One approach for aligning antenna polarization for a VSAT system is provided by Hughes Network Solutions, LLC. Hughes provides outdoor pointing interface (OPI) operating instructions that provide feedback from the pointing software to the installer at the VSAT system during the pointing process. However, Hughes OPI still allows the remote satellite terminal to operate satisfactory with the co-polarized receive gain even if the cross polarized transmit gain is not aligned correctly, which causes cross polarization interference at the satellite.
Other automated or non-interventional techniques have been developed that replicate the function of the Network Operator robotically. These techniques, while reducing the burden on the Network Operations centers, and at times successfully enforcing cross polarization discipline amongst the installers, are typically very complex and expensive to implement, and suffer from many of the same scalability problems as the normal procedure of human intervention.